A simple algorithm for in vivo ocular fundus oximetry compensating for non-haemoglobin absorption and scattering

An algorithm is introduced for the compensation of the influence of non-haemoglobin absorption as well as tissue scattering on blood spectra used in optical oximetry at the ocular fundus. The in vivo measured spectra were corrected by a linear transformation in order to match the reference spectra of fully oxygenated and reduced blood, respectively, at three isosbestic points (522 nm, 569 nm and 586 nm). The oxygen saturation can then be determined at a wavelength showing a high contrast between oxygenated and reduced haemoglobin (e.g., 560 nm). Reflection measurements at blood flowing through cuvettes were used to validate the algorithm. The oxygen saturation values were compared to measurements of the same samples at a laboratory haemoximeter. The mean deviation was found to be 2.65%.